Sorting It All Out. Why Classify?

1 What You Will Learn Explain why and how organisms are classified. List the eight levels of classification. Explain scientific names. Describe how dichotomous keys help in identifying organisms. Vocabulary classification taxonomy dichotomous key READING STRATEGY Reading Organizer As you read this section, create an outline of the section. Use the headings from the section in your outline. classification the division of organisms into groups, or classes, based on specific characteristics Sorting It All Out Imagine that you live in a tropical rain forest and must get your own food, shelter, and clothing from the forest. What do you need to know to survive in the forest? To survive in the rain forest, you need to know which plants are safe to eat and which are not. You need to know which animals you can eat and which might eat you. In other words, you need to study the living things around you and organize them into categories, or classify them. Classification is putting things into orderly groups based on similar characteristics. Why Classify? For thousands of years, humans have classified living things based on usefulness. The Chácabo people of Bolivia know of 360 types of plants that grow in the forest where they live. Of these 360 plant types, 305 are useful to the Chácabo. Some biologists, such as those shown in Figure 1, classify living and extinct organisms. Scientists classify organisms to help make sense and order of the many kinds of living things in the world. Biologists use a system to classify living things. This system groups organisms according to the characteristics they share. The classification of living things makes it easier for biologists to answer many important questions, such as the following: How many known species are there? What are the defining characteristics of each species? What are the relationships between these species? Reading Check What are three questions that classifying organisms can help answer? (See the Appendix for answers to Reading Checks.) Figure 1 These biologists are sorting rain-forest plant material. 164 Chapter 7

Platypus Brown Bear Lion House Cat Retractable claws Ability to purr Figure 2 This branching diagram shows the similarities and differences between four mammals. Giving birth to live young Hair, mammary glands How Do Scientists Classify Organisms? Before the 1600s, many scientists divided organisms into two groups: plants and animals. But as more organisms were discovered, some did not fit into either group. In the 1700s, Carolus Linnaeus (KAR uh luhs li NAY uhs), a Swedish scientist, founded modern taxonomy. Taxonomy (taks AHN uh mee) is the science of describing, classifying, and naming living things. Linnaeus tried to classify all living things based on their shape and structure. Today, scientists use a system of classification that is very similar to the one that Linnaeus developed. Classification Today Taxonomists use an eight-level system to classify living things based on shared characteristics. Scientists also use shared characteristics to hypothesize how closely related living things are. The more characteristics the organisms share, the more closely related the organisms may be. For example, the platypus, brown bear, lion, and house cat are thought to be related because they share many characteristics. These animals have hair and mammary glands, so they are grouped together as mammals. But they can be further classified into more-specific groups. Branching Diagrams Look at the branching diagram in Figure 2. Several characteristics are listed along the line that points to the right. Each characteristic is shared by the animals to the right of it. All of the animals shown have hair and mammary glands. But only the bear, lion, and house cat give birth to live young. The lion and the house cat have retractable claws, but the other animals do not. Thus, the lion and the house cat are more closely related to each other than to the other animals. taxonomy the science of describing, naming, and classifying organisms A Branching Diagram 1. Construct a diagram similar to the one in Figure 2. 2. Use a frog, a snake, a kangaroo, and a rabbit in your diagram. 3. Think of one major change that happened before the frog evolved. 4. For the last three organisms, think of a change that happened between one of these organisms and the other two. Write all of these changes in your diagram. Section 1 Sorting It All Out 165

For another activity related to this chapter, go to go.hrw.com and type in the keyword HL5CLSW. Figure 3 The eight levels of classification are domain, kingdom, phylum, class, order, family, genus, and species. Levels of Classification Every living thing is classified into one of three domains. Domains are the largest and most general groups. All living things in a domain are sorted into kingdoms. The members of one kingdom are more like each other than they are like the members of another kingdom. All living things in a kingdom are further sorted into phyla (singular, phylum). The members of a phylum are sorted into classes. Each class includes one or more orders. Orders are separated into families. Families are broken into genera (singular, genus). And genera are sorted into species. A species is a group of organisms that are closely related and can mate to produce fertile offspring. Figure 3 shows the classification of a house cat from the kingdom Animalia to the species Felis domesticus. Scientific Names By classifying organisms, biologists can give organisms scientific names. A scientific name remains the same for a specific kind of organism even if the organism has many common names. Before Linnaeus s time, scholars used names that were as long as 12 words to identify species. This system was hard to work with because the names were so long. The system was also hard to use because individual scientists named organisms differently. So, an organism could have more than one name. Kingdom Animalia Phylum Chordata Class Mammalia Order Carnivora All animals are in the kingdom Animalia. All animals in the phylum Chordata have a hollow nerve cord. Most have a backbone. Animals in the class Mammalia have a backbone. They also nurse their young. Animals in the order Carnivora have a backbone and nurse their young. They also have special teeth for tearing meat. 166 Chapter 7 Classification

Two-Part Names Linnaeus simplified the naming of living things by giving each species a two-part scientific name. For example, the scientific name for the Asian elephant is Elephas maximus (EL uh fuhs MAK suh muhs). The first part of the name, Elephas, is the genus name. The second part, maximus, is the specific name. No other species has the name Elephas maximus. Naming rules help scientists communicate clearly about living things. All genus names begin with a capital letter. All specific names begin with a lowercase letter. Usually, both words are underlined or italicized. But if the surrounding text is italicized, the scientific name is not, as Figure 4 shows. These printing styles show a reader which words are the scientific name. Scientific names, which are usually in Latin or Greek, contain information about an organism. The name of the animal shown in Figure 4 is Tyrannosaurus rex. Tyrannosaurus is a combination of two Greek words and means tyrant lizard. The word rex is Latin for king. The name tells you that this animal was probably not a passive grass eater! Sometimes, Tyrannosaurus rex is referred to as T. rex. To be correct, the scientific name must consist of the genus name (or its abbreviation) and the specific name. Reading Check What are the two parts of a scientific name? Figure 4 You would never call Tyrannosaurus rex just rex! Family Felidae Animals in the family Felidae are cats. They have a backbone, nurse their young, have special teeth for tearing meat, and have retractable claws. Genus Felis Animals in the genus Felis have traits of other animals in the same family. However, these cats cannot roar; they can only purr. Species Felis domesticus The species Felis domesticus is the common house cat. The house cat shares traits with all of the organisms in the levels above the species level, but it also has unique traits. Section 1 Sorting It All Out 167

dichotomous key an aid that is used to identify organisms and that consists of the answers to a series of questions Dichotomous Keys You might someday turn over a rock and find an organism that you don t recognize. How would you identify the organism? Taxonomists have developed special guides to help scientists identify organisms. A dichotomous key (die KAHT uh muhs KEE) is an identification aid that uses sequential pairs of descriptive statements. There are only two alternative responses for each statement. From each pair of statements, the person trying to identify the organism chooses the statement that describes the organism. Either the chosen statement identifies the organism or the person is directed to another pair of statements. By working through the statements in the key in order, the person can eventually identify the organism. Using the simple dichotomous key in Figure 5, try to identify the two animals shown. Reading Check What is a dichotomous key? Figure 5 A dichotomous key can help you identify organisms. 1. a. This mammal flies. Its hand forms a wing. little brown bat b. This mammal does not fly. It s hand does not form a wing. Go to step 2. 2. a. This mammal has no hair on its tail. Go to step 3. b. This mammal has hair on its tail. Go to step 4. 3. a. This mammal has a short, naked tail. eastern mole b. This mammal has a long, naked tail. Go to step 5. 4. a. This mammal has a black mask across its face. raccoon b. This mammal does not have a black mask across its face. Go to step 6. 5. a. This mammal has a tail that is flat and paddle shaped. beaver b. This mammal has a tail that is not flat or paddle shaped. opossum 6. a. This mammal is brown and has a white underbelly. Go to step 7. b. This mammal is not brown and does not have a white underbelly. Go to step 8. 7. a. This mammal has a long, furry tail that is black on the tip. longtail weasel b. This mammal has a long tail that has little fur. white-footed mouse 8. a. This mammal is black and has a narrow white stripe on its forehead and broad white stripes on its back. striped skunk b. This mammal is not black and does not have white stripes. Go to step 9. 9. a. This mammal has long ears and a short, cottony tail. eastern cottontail b. This mammal has short ears and a medium-length tail. woodchuck 168 Chapter 7 Classification

A Growing System You may think that all of the organisms on Earth have already been classified. But people are still discovering and classifying organisms. Some newly discovered organisms fit into existing categories. But sometimes, someone discovers new evidence or an organism that is so different from other organisms that it does not fit existing categories. For example, in 1995, scientists studied an organism named Symbion pandora (SIM bee AHN pan DAWR uh). Scientists found S. pandora living on lobster lips! Scientists learned that S. pandora had some characteristics that no other known organism had. In fact, scientists trying to classify S. pandora found that it didn t fit in any existing phylum. So, taxonomists created a new phylum for S. pandora. Review Summary In classification, organisms are grouped according to the characteristics the organisms share. Classification lets scientists answer important questions about the relationships between organisms. The eight levels of classification are domain, kingdom, phylum, class, order, family, genus, and species. An organism has one two-part scientific name. A dichotomous key is a tool for identifying organisms that uses a series of paired descriptive statements. Using Key Terms 1. In your own words, write a definition for each of the following terms: classification and taxonomy. Understanding Key Ideas 2. The two parts of a scientific name are the names of the genus and the a. specific name. b. phylum name. c. family name. d. order name. 3. Why do scientists use scientific names for organisms? 4. List the eight levels of classification. 5. Describe how a dichotomous key helps scientists identify organisms. Critical Thinking 6. Analyzing Processes Biologists think that millions of species are not classified yet. Why do you think so many species have not been classified yet? 7. Applying Concepts Both dolphins and sharks have a tail and fins. How can you determine if dolphins and sharks are closely related? Interpreting Graphics Use the figure below to answer the questions that follow. Moss Fern Pine tree Hibiscus Seeds Flowers Tissues that transport materials Ability to live on land 8. Which plant is most similar to the hibiscus? 9. Which plant is least similar to the hibiscus? For a variety of links related to this chapter, go to www.scilinks.org Topic: Basis for Classification; Levels of Classification SciLinks code: HSM0138; HSM0870 169

2 What You Will Learn Explain how classification developed as greater numbers of organisms became known. Describe the three domains. Describe four kingdoms in the domain Eukarya. Vocabulary Archaea Bacteria Eukarya Protista Fungi Plantae Animalia READING STRATEGY Discussion Read this section silently. Write down questions that you have about this section. Discuss your questions in a small group. Figure 1 How would you classify this organism? This member of the genus Euglena, which is shown here highly magnified, has characteristics of both plants and animals. Domains and Kingdoms What do you call an organism that is green, makes its own food, lives in pond water, and moves? Is it a plant, an animal, or something in between? For hundreds of years, all living things were classified as either plants or animals. But over time, scientists discovered species that did not fit easily into these two kingdoms. For example, an organism of the genus Euglena, such as the one shown in Figure 1, has characteristics of both plants and animals. How would you classify such an organism? What Is It? Organisms are classified by their characteristics. For example, euglenoids, which include members of the genus Euglena, have the following characteristics: Euglenoids are single celled and live in pond water. Euglenoids are green and make their own food by photosynthesis. These characteristics might lead you to conclude that euglenoids are plants. However, you should consider the following characteristics of euglenoids: Euglenoids move by whipping their tails, which are called flagella. Euglenoids can feed on other organisms. Plants do not move around and usually do not eat other organisms. So, are euglenoids animals? As you can see, euglenoids do not fit into plant or animal categories. Scientists solved this classification problem by adding another kingdom kingdom Protista to classify organisms such as euglenoids. As scientists learned more about living things, they changed the classification system. Today, there are three domains in the classification system. Domains represent the largest differences between organisms. These domains are divided into several kingdoms. 170 Chapter 7 Classification

Figure 2 The Grand Prismatic Spring in Yellowstone National Park contains water that is about 90 C (194 F). The spring is home to archaea that thrive in its hot water. The Domain Archaea The domain Archaea (ahr KEE uh) is made up entirely of archaea. Archaea are one of two kinds of prokaryotes (proh KAR ee OHTS). Prokaryotes are single-celled organisms that do not have a nucleus. Archaea were first discovered living in extreme environments, where other organisms could not survive. Figure 2 shows a hot spring in Yellowstone National Park. The yellow and orange rings around the edge of the hot spring are made up of billions of archaea. Some archaea can also be found in moderate environments, such as the open ocean. Reading Check Describe one characteristic of an organism in the domain Archaea. The Domain Bacteria All bacteria (bak TEER ee uh) belong to the domain Bacteria. Bacteria are another kind of prokaryote. Bacteria can be found in soil, water, and even on and inside the human body! For example, Escherichia coli (ESH uh RIK ee uh KOH LIE), shown in Figure 3, is present in large numbers in human intestines, where it produces vitamin K. One kind of bacterium converts milk into yogurt. Some bacteria cause diseases, such as pneumonia. Other bacteria make chemicals that help humans fight disease-causing bacteria. Archaea in a modern taxonomic system, a domain made up of prokaryotes (most of which are known to live in extreme environments) that are distinguished from other prokaryotes by differences in their genetics and in the makeup of their cell wall; this domain aligns with the traditional kingdom Archaebacteria Bacteria in a modern taxonomic system, a domain made up of prokaryotes that usually have a cell wall and that usually reproduce by cell division; this domain aligns with the traditional kingdom Eubacteria Figure 3 Specimens of E. coli are shown on the point of a pin under a scanning electron microscope. These bacteria live in the intestines of animals and decompose undigested food. 171

The Domain Eukarya All organisms whose cells have a nucleus and membrane-bound organelles are called eukaryotes. Eukaryotes belong to the domain Eukarya. Four kingdoms currently make up the domain Eukarya: Protista, Fungi, Plantae, and Animalia. Figure 4 This slime mold is a protist. Eukarya in a modern taxonomic system, a domain made up of all eukaryotes; this domain aligns with the traditional kingdoms Protista, Fungi, Plantae, and Animalia The Kingdom Protista Today, members of the kingdom Protista (proh TIST uh), commonly called protists, are single-celled or simple multicellular organisms. Scientists think that the first protists evolved from ancient bacteria about 2 billion years ago. Eventually, ancient protists gave rise to fungi, plants, and animals. The kingdom Protista contains many kinds of organisms. Some animal-like protists are called protozoans. Some plantlike protists are called algae. Protists also include slime molds, such as the one shown in Figure 4, and euglenoids. The Kingdom Fungi Molds and mushrooms are examples of the complex, multicellular members of the kingdom Fungi (FUHN JIE). Unlike plants, fungi do not perform photosynthesis. Unlike animals, fungi do not eat food. Instead, fungi absorb nutrients from substances in their surroundings. They use digestive juices to break down the substances. Figure 5 shows a very poisonous fungus. Never eat wild fungi. Figure 5 This beautiful fungus of the genus Amanita is poisonous. 172 Chapter 7

Figure 6 Giant sequoias can measure 30 m around at the base and can grow to more than 91.5 m tall. Figure 7 Plants such as these are common in the Tropics. The Kingdom Plantae Although plants vary remarkably in size and form, most people easily recognize the members of the kingdom Plantae. Plantae consists of organisms that are eukaryotic, have cell walls, and make food through photosynthesis. For photosynthesis to occur, plants must be exposed to sunlight. Plants can therefore be found on land and in water that light can penetrate. The food that plants make is important not only for the plants but also for all of the organisms that get nutrients from plants. Most life on Earth is dependent on plants. For example, some fungi, protists, and bacteria consume plants. When these organisms digest the plant ma terial, they get energy and nutrients made by the plants. Plants also provide habitat for other organisms. The giant sequoias in Figure 6 and the flowering plants in Figure 7 provide birds, insects, and other animals with a place to live. Reading Check How do plants provide energy and nutrients to other organisms? Plantae a kingdom made up of complex, multicellular organisms that are usually green, have cell walls made of cellulose, cannot move around, and use the sun s energy to make sugar by photosynthesis Ring-Around-the-Sequoia How many students would have to join hands to form a human chain around a giant sequoia that is 30 m in circumference? Assume for this calculation that the average student can extend his or her arms about 1.3 m. Section 2 Domains and Kingdoms 173

Animalia a kingdom made up of complex, multicellular organisms that lack cell walls, can usually move around, and quickly respond to their environment The Kingdom Animalia The kingdom Animalia contains complex, multicellular organisms that don t have cell walls, are usually able to move around, and have specialized sense organs. These sense organs help most animals quickly respond to their environment. Organisms in the kingdom Animalia are commonly called animals. You probably recognize many of the organisms in the kingdom Animalia. All of the organisms in Figure 8 are animals. Animals depend on the organisms from other kingdoms. For example, animals depend on plants for food. Animals also depend on bacteria and fungi to recycle the nutrients found in dead organisms. Figure 8 The kingdom Animalia contains many different organisms, such as eagles, tortoises, and beetles. WRITING Animals That Help Humans have depended on SKILL animals for thousands of years. Many people around the world still use oxen to farm. Camels, horses, donkeys, goats, and llamas are all still used as pack animals. Dogs still help herd sheep, protect property, and help people hunt. Scientists are even discovering new ways that animals can help us. For example, scientists are training bees to help find buried land mines. Using the library or the Internet, research an animal that helps people. Make a poster describing the animal and the animal s scientific name. The poster should show who uses the animal, how the animal is used, and how long people have depended on the animal. Find or draw pictures to put on your poster. 174 Chapter 7 Classification

Strange Organisms Classifying organisms is often not easy. Like animals, some plants can eat other organisms to obtain nutrients. Some protists can use photosynthesis as plants do and can move around as animals do. The kingdom Animalia also includes members that might surprise you, such as worms, insects, and corals. The red cup sponge in Figure 9 is also an animal. Sponges are usually considered the simplest animals. They lack sense organs, and most of them cannot move. Scientists used to classify sponges as plants. But sponges cannot make their own food. They must eat other organisms to get nutrients, which is one reason that sponges are classified as animals. Figure Reading Check Why were sponges once thought to be plants? 9 This red cup sponge is a simple animal. Review Summary In the past, organisms were classified as plants or animals. As scientists discovered more species, they found that organisms did not always fit into one of these two categories, so they changed the classification system. Today, domains are the largest groups of related organisms. The three domains are Archaea and Bacteria, both of which consist of prokaryotes, and Eukarya, which consists of eukaryotes. The kingdoms of the domain Eukarya are Protista, Fungi, Plantae, and Animalia. Using Key Terms For each pair of terms, explain how the meanings of the terms differ. 1. Archaea and Bacteria 2. Plantae and Fungi Understanding Key Ideas 3. Biological classification schemes change a. as new evidence and more kinds of organisms are discovered. b. every 100 years. c. when scientists disagree. d. only once. 4. Describe the characteristics of each of the three domains. 5. Describe the four kingdoms of domain Eukarya. Math Skills 6. A certain bacterium can divide every 30 min. If you begin with 1 bacterium, when will you have more than 1,000 bacteria? Critical Thinking 7. Identifying Relationships How are bacteria similar to fungi? How are fungi similar to animals? 8. Analyzing Methods Why do you think Linnaeus did not include classification kingdoms for categories of archaea and bacteria? 9. Applying Concepts The Venus flytrap does not move around. It can make its own food by using photosynthesis. It can also trap insects and digest the insects to get nutrients. The flytrap also has a cell wall. Into which kingdom would you place the Venus flytrap? What makes this organism unusual in the kingdom you chose? For a variety of links related to this chapter, go to www.scilinks.org Topic: Kingdoms SciLinks code: HSM1397 175

Complete each of the following sentences by choosing the correct term from the word bank. Animalia Protista Bacteria Plantae Archaea classification taxonomy 1 Linnaeus founded the science of. 2 Prokaryotes that live in extreme environments are in the domain. 3 Complex multicellular organisms that can usually move around and respond to their environment are in the kingdom. 4 A system of can help group animals into categories. 5 Prokaryotes that can cause diseases are in the domain. Multiple Choice USING KEY TERMS UNDERSTANDING KEY IDEAS 6 Scientists classify organisms by a. arranging the organisms in orderly groups. b. giving the organisms many common names. c. deciding whether the organisms are useful. d. using only existing categories of classification. 7 When the eight levels of classification are listed from broadest to narrowest, which level is sixth in the list? a. class b. order c. genus d. family 8 The scientific name for the European white waterlily is Nymphaea alba. To which genus does this plant belong? a. Nymphaea c. water lily b. alba d. alba lily 9 Animalia, Protista, Fungi, and Plantae are the a. scientific names of different organisms. b. names of kingdoms. c. levels of classification. d. scientists who organized taxonomy. 0 The simple, single-celled organisms that live in your intestines are classified in the domain a. Protista. c. Archaea. b. Bacteria. d. Eukarya. q What kind of organism thrives in hot springs and other extreme environments? a. fungus c. archaean b. bacterium d. protist 178 Chapter 7 Classification

Short Answer w Why is the use of scientific names important in biology? e What kind of evidence is used by modern taxonomists to classify organisms based on evolutionary relationships? INTERPRETING GRAPHICS Use the branching diagram of selected primates below to answer the questions that follow. r Is a bacterium a type of eukaryote? Explain your answer t Scientists used to classify organisms as either plants or animals. Why doesn t that classification system work? Lemur Baboon Chimpanzee D Human CRITICAL THINKING y Concept Mapping Use the following terms to create a concept map: kingdom, fern, lizard, Animalia, Fungi, algae, Protista, Plantae, and mushroom. u Analyzing Methods Explain how the levels of classification depend on the similarities and differences between organisms. i Making Inferences Explain why two species that belong to the same genus, such as white oak (Quercus alba) and cork oak (Quercus suber), also belong to the same family. o Identifying Relationships What characteristics do the members of the four kingdoms of the domain Eukarya have in common? A Bipedal, language p Which primate is the closest relative to the common ancestor of all primates? a Which primate shares the most traits with humans? s Do both lemurs and humans have the characteristics listed at point D? Explain your answer. d What characteristic do baboons have that lemurs do not have? Explain your answer. B C Much larger brain Color vision Binocular vision, opposable thumbs Chapter Review 179

READING Read each of the passages below. Then, answer the questions that follow each passage. Passage 1 When organizing life on Earth into categories, we must remember that organisms are not equally distributed throughout the categories of our classification system. We often think of Earth s living things as only the plants and animals that live on Earth s surface. However, the largest domains in terms of the number of individuals and total mass are the domains Archaea and Bacteria. And a common home of archaea and bacteria may be deep within the Earth s crust. 1. In the passage, what does distributed mean? A divided B important C visible D variable 2. According to the passage, what are most of the organisms living on Earth? F plants G animals H fungi I archaea and bacteria 3. Which of the following statements is a fact according to the passage? A All organisms are equally distributed over Earth s surface. B Plants are the most important organisms on Earth. C Many archaea and bacteria may live deep within Earth s crust. D Archaea and bacteria are equally distributed over Earth s surface. Passage 2 When you think of an animal, what do you imagine? You may think of a dog, a cat, or a parrot. All of those organisms are animals. But the animal kingdom also includes some members that might surprise you, such as worms, insects, corals, and sponges. 1. In the passage, what is coral? A a kind of animal B a kind of insect C a color similar to pink D an organism found in lakes and streams 2. What can you infer from the passage? F All members of the animal kingdom are visible. G Parrots make good pets. H Not all members of the animal kingdom have DNA. I Members of the animal kingdom come in many shapes and sizes. 3. Which of the following can you infer from the passage? A Worms and corals make good pets. B Corals and cats have some traits in common. C All organisms are animals. D Worms, corals, insects, and sponges are in the same family. 4. In the passage, what does members mean? F teammates G limbs H individuals admitted to a club I components 180 Chapter 7 Classification

INTERPRETING GRAPHICS The Venn diagrams below show two classification systems. Use the diagrams to answer the questions that follow. Classification system A 1 2 3 4 5 6 7 Classification system B 4. For Classification system B, which of the following statements is true? F All organisms in group 4 are in group 1, 2, and 5. G All organisms in group 4 are in groups 3 and 5. H All organisms in group 4 are in groups 5 and 6. I All organisms in group 4 are in groups 1, 5, and 6. 5. In Classification system B, which group contains organisms that are not in group 1? A 2 B 4 C 5 D 6 1 2 3 4 5 6 MATH Read each question below, and choose the best answer. 1. For Classification system A, which of the following statements is true? A All organisms in group 6 are in group 7. B All organisms in group 5 are in group 4. C All organisms in group 6 are in group 1. D All organisms in group 2 are in group 1. 2. For Classification system A, which of the following statements is true? F All organisms in group 3 are in group 2. G All organisms in group 3 are in group 4. H All organisms in group 3 are in group 1. I All organisms in group 3 are in every other group. 3. For Classification system B, which of the following statements is true? A All organisms in group 1 are in group 6. B All organisms in group 6 are in group 1. C All organisms in group 3 are in group 1. D All organisms in group 2 are in group 5. 1. Scientists estimate that millions of species have not yet been discovered and classified. About 1.8 million species have been discovered and classified. If scientists think that this 1.8 million makes up only 10% of the total number of species on Earth, how many species do scientists think exist on Earth? A 180 million B 18 million C 1.8 million D 180,000 2. Sequoia trees can grow to more than 90 m in height. There are 3.28 feet in 1 meter. How many feet are in 90 m? F 27.4 ft G 95.2 ft H 270 ft I 295.2 ft Standardized Test Preparation Standardized Test Preparation 181